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Chemistry

Ca, Mg, P, Fe, TIBC

Beyond the major electrolytes (\(Na\), \(K\), \(Cl\), bicarbonate), calcium, magnesium, phosphorus, and iron are vital for numerous physiological processes. They are crucial for nerve and muscle function, bone health, enzyme activity, and oxygen transport

Electrolytes

  • Definition: Ions (charged particles) that conduct electrical impulses in solution. These electrolytes are essential for various physiological processes
  • Key Electrolytes
    • Calcium (\(Ca^{2+}\))
    • Magnesium (\(Mg^{2+}\))
    • Phosphorus (\(P\))
    • Iron (\(Fe\))
  • Normal Ranges:
    • Calcium (\(Ca^{2+}\)): 8.6-10.2 mg/dL or 2.2-2.6 mmol/L (SI units)
    • Magnesium (\(Mg^{2+}\)): 1.7-2.2 mg/dL or 0.70-0.90 mmol/L (SI units)
    • Phosphorus (\(P\)): 2.5-4.5 mg/dL or 0.81-1.45 mmol/L (SI units)
    • Iron (\(Fe\)): 60-170 μg/dL or 10.7-30.4 μmol/L (SI units)
    • Total Iron-Binding Capacity (TIBC): 240-450 μg/dL or 42.9-80.6 μmol/L (SI units)

Calcium (\(Ca^{2+}\))

  • Distribution
    • Bone: Approximately 99% of calcium is stored in bone as hydroxyapatite
    • Blood: Approximately 1% of calcium is in the blood
      • Ionized (Free) Calcium: The physiologically active form (45%)
      • Protein-Bound Calcium: Bound to albumin (40%)
      • Complexed Calcium: Complexed with anions (e.g., phosphate, citrate) (15%)
  • Regulation
    • Parathyroid Hormone (PTH): Increases blood calcium levels by stimulating bone resorption, increasing kidney reabsorption, and increasing vitamin D activation
    • Vitamin D: Increases blood calcium levels by promoting calcium absorption from the intestine
    • Calcitonin: Decreases blood calcium levels by inhibiting bone resorption
  • Functions
    • Bone Structure: Essential for bone formation and maintenance
    • Muscle Contraction: Triggers muscle contraction
    • Nerve Function: Involved in nerve impulse transmission
    • Blood Clotting: Required for the coagulation cascade
    • Enzyme Activity: Acts as a cofactor for certain enzymes
    • Cell Signaling: Involved in various cell signaling pathways
  • Pathophysiology of Abnormal Levels
    • Hypercalcemia: High calcium levels due to hyperparathyroidism, malignancy, or vitamin D excess
    • Hypocalcemia: Low calcium levels due to hypoparathyroidism, vitamin D deficiency, or kidney disease

Magnesium (\(Mg^{2+}\))

  • Distribution
    • Bone: Approximately 60% of magnesium is stored in bone
    • Intracellular Fluid (ICF): Approximately 39% is in the ICF
    • Blood: Approximately 1% is in the blood
      • Ionized (Free) Magnesium: The physiologically active form
      • Protein-Bound Magnesium: Bound to albumin
      • Complexed Magnesium: Complexed with anions
  • Regulation
    • Kidneys: Regulate magnesium reabsorption and excretion
    • Parathyroid Hormone (PTH): Influences magnesium reabsorption in the kidneys
  • Functions
    • Enzyme Activity: Acts as a cofactor for many enzymes, including those involved in ATP production
    • Muscle and Nerve Function: Important for nerve impulse transmission and muscle contraction
    • Bone Health: Contributes to bone structure and strength
    • DNA and Protein Synthesis: Required for DNA and protein synthesis
  • Pathophysiology of Abnormal Levels
    • Hypermagnesemia: High magnesium levels due to kidney disease or excessive magnesium intake
    • Hypomagnesemia: Low magnesium levels due to poor dietary intake, impaired absorption, or increased excretion

Phosphorus (\(P\))

  • Distribution
    • Bone: Approximately 85% of phosphorus is stored in bone as hydroxyapatite
    • Intracellular Fluid (ICF): Most of the remainder is located within cells
    • Blood: A small amount is in the blood as inorganic phosphate
  • Regulation
    • Parathyroid Hormone (PTH): Decreases blood phosphate levels by increasing kidney excretion and increasing bone turnover
    • Vitamin D: Increases blood phosphate levels by promoting intestinal absorption and bone resorption
    • Fibroblast Growth Factor 23 (FGF23): Decreases blood phosphate levels by increasing kidney excretion and decreasing intestinal absorption
  • Functions
    • Bone Structure: Essential for bone formation and maintenance
    • Energy Production: Involved in ATP production
    • DNA and RNA Synthesis: Required for DNA and RNA synthesis
    • Cell Membrane Structure: Component of phospholipids
    • pH Balance: Acts as a buffer in the blood
  • Pathophysiology of Abnormal Levels
    • Hyperphosphatemia: High phosphate levels due to kidney disease, hypoparathyroidism, or excessive phosphate intake
    • Hypophosphatemia: Low phosphate levels due to poor dietary intake, impaired absorption, or increased excretion

Iron (\(Fe\))

  • Distribution
    • Hemoglobin: Approximately 70% of iron is in hemoglobin
    • Ferritin: Approximately 25% of iron is stored as ferritin in the liver, spleen, and bone marrow
    • Transferrin: A small amount of iron is transported in the blood bound to transferrin
  • Regulation
    • Absorption: Iron absorption in the small intestine is regulated by hepcidin
    • Storage: Iron is stored in cells as ferritin or hemosiderin
    • Transport: Iron is transported in the blood bound to transferrin
  • Functions
    • Oxygen Transport: Component of hemoglobin and myoglobin, which transport oxygen in the blood and muscles
    • Enzyme Activity: Acts as a cofactor for many enzymes, including those involved in energy production and DNA synthesis
  • Pathophysiology of Abnormal Levels
    • Iron Deficiency Anemia: Low iron levels due to poor dietary intake, impaired absorption, or blood loss
    • Hemochromatosis: Excessive iron absorption and accumulation in tissues

Total Iron-Binding Capacity (TIBC)

  • Definition: A measure of the blood’s capacity to bind iron with transferrin
  • Interpretation
    • Elevated TIBC: Suggests iron deficiency
    • Decreased TIBC: Suggests iron overload or chronic inflammation
  • Calculation
    • Indirectly used to calculate transferrin saturation
      • Transferrin Saturation (%) = (Serum Iron / TIBC) x 100

Key Terms

  • Electrolyte: An ion that conducts electrical impulses in solution
  • Cation: A positively charged ion (e.g., \(Ca^{2+}\), \(Mg^{2+}\), \(K^+\), \(Na^+\))
  • Anion: A negatively charged ion (e.g., \(Cl^-\), \(HCO_3^-\), \(PO_4^{3-}\))
  • Parathyroid Hormone (PTH): A hormone that increases blood calcium levels
  • Vitamin D: A hormone that increases blood calcium and phosphate levels
  • Calcitonin: A hormone that decreases blood calcium levels
  • Fibroblast Growth Factor 23 (FGF23): A hormone that decreases blood phosphate levels
  • Hydroxyapatite: The mineral component of bone
  • Hemoglobin: A protein in red blood cells that transports oxygen
  • Myoglobin: A protein in muscle cells that stores oxygen
  • Ferritin: A protein that stores iron
  • Transferrin: A protein that transports iron in the blood
  • Total Iron-Binding Capacity (TIBC): A measure of the blood’s capacity to bind iron
  • Transferrin Saturation: The percentage of transferrin that is bound to iron
  • Hepcidin: A hormone that regulates iron absorption and release
  • Hypercalcemia: Abnormally high calcium in the blood
  • Hypocalcemia: Abnormally low calcium in the blood
  • Hypermagnesemia: Abnormally high magnesium in the blood
  • Hypomagnesemia: Abnormally low magnesium in the blood
  • Hyperphosphatemia: Abnormally high phosphorus in the blood
  • Hypophosphatemia: Abnormally low phosphorus in the blood
  • Hypoferremia: Abnormally low iron in the blood
  • Hemochromatosis: A genetic disorder of iron overload
  • Hypoxia: An inadequate oxygen supply to the cells and tissues of the body
  • Muscle Contraction: The shortening of muscle cells
  • Nerve Function: The function of neurons and their role in nerve impluse transmittion
  • Blood Clotting: The coagulation of blood